The present invention relates to an optical device used in optical communication and to a manufacturing method therefor.
There is increasing demand for faster, more densely integrated optical interconnects that consume less power when propagating light over short distances between chips in order to realize exascale computers able to perform 1018 calculations per second. Silicon photonics is a technology essential to meeting this demand. In silicon photonics, fine optical waveguides are created from silicon, and circuits composed of these optical waveguides are used as a platform.
An optical waveguide created using silicon photonics has a core serving as the optical path for propagating light, and cladding which covers the core. The cladding is designed to totally reflect light, confine the light inside the core, and enable light to be propagated without loss. Therefore, the optical waveguide requires a structure in which the light propagating through the waveguide is prevented from leaking towards the silicon substrate.
In this structure, a SiO2 layer referred to as buried oxide layer is generally used as lower cladding for the optical waveguide (see, for example, the publication of Yasuhiko Arakawa, et al., “Silicon Photonics for Next Generation System Integration Platform”, IEEE Communications Magazine, pp. 72-77, March 2013). An example of this structure is shown in FIG. 1. The structure shown in FIG. 1 includes a Si substrate 10, a SiO2 layer 11 forming the lower cladding on top of the Si substrate 10, and a Si waveguide 12 formed on top of the SiO2 layer. The SiO2 layer 11 is formed to a thickness, for example, 2 μm, sufficient to prevent light propagating through the Si waveguide 12 from leaking towards the Si substrate 10.
Another structure is known in which the SiO2 layer is etched away to form an air bridge in the Si waveguide which has an improved light confinement effect (see, for example, Laid-open Patent Publication No. 2003-215519, Laid-open Patent Publication No. 2004-341147, and the publication of Solomon Assefa, et al., “A 90-nm CMOS Integrated Nano-Photonics Technology for 25 Gbps WDM Optical Communications Applications”, IEEE International Electronic Devices Meeting, Post Deadline Session 33.8, Dec. 10-12, 2012). An example of this structure is shown in FIG. 2. The structure shown in FIG. 2 includes a Si substrate 10, a SiO2 layer 11 on top of the Si substrate 10, an air layer 13 formed inside the SiO2 layer 11, and a Si waveguide 12 supported by the surface of the SiO2 layer and formed above the air layer 13. The air layer 13 is formed to a thickness, for example, 2 μm, sufficient to prevent light propagating through the Si waveguide 12 from leaking towards the Si substrate 10.